Producers of gas turbine engines have made great strides in reducing regulated emissions such as NOx. However, these strides have led to various instabilities in combustion, such as combustor thermo-acoustic oscillations. This problem may be brought about by the coupling of the heat release and pressure waves, which produce a resonance with a characteristic frequency usually corresponding to one or more natural frequencies of the combustion chamber. This has been historically described by the well-known Rayleigh Mechanism. Such oscillations in the combustor may result in mechanical and thermal fatigue to combustor hardware which may lead to other operational problems that may have adverse affects on the engine.
Several attempts have been made to eliminate, diminish or prevent thermo-acoustic oscillations. One such attempt to attenuating oscillations was to decouple the heat release form the pressure wave by moving the fuel introduction point in the injector so that the residence time to the flame was different than that required to sustain resonant oscillations. This may be accomplished by moving the fuel spokes along the length of the injector main fuel and air flow path.
Another attempt to attenuate oscillations was to introduce airflow in a row of holes around the circumference of the injector barrel. The axial location of the row of holes along the barrel was determined so as to dilute the fuel to air ratio in an attempt to provide a non-sinusoidal variation in the energy input to the flame. However, problems with such attempts has been in the limited number of frequencies of oscillations that could be attenuated. Unfortunately, some engines exhibit more than one frequency of oscillation when they are at different power settings.
The system and method of the present disclosure is set forth to overcome at least one of the problems described above.